Receive data on the other end.

I added a bunch of receipt interfaces, but I only test the syncronous
message receipt at the moment, not fragments or async.

I'm not sure whether 'subscribe_message' even makes sense as a concept,
but there it is.

src/msp_channel.erl

@@ -10,7 +10,13 @@
 -license("MIT").
 
 -export([configure_channel/4]).
--export([send_and_close/2]).
+-export([send_and_close/2, send_message/2]).
+% A lot of interfaces, but the last two are only really written for
+% completeness. The distinctions here are blocking vs subscribing, and
+% fragments vs messages.
+-export([receive_fragment/1, receive_message/1,
+         subscribe_fragment/1, subscribe_message/1,
+         subscribe_fragment_once/1, subscribe_message_once/1]).
 
 %% gen_server
 -export([start_link/0]).
@@ -24,30 +30,21 @@
 % Fragment/message opcodes:
 % _____________________________________________________________________________
 % OP_FRAGMENT     | Part of a message/stream
-% OP_OPEN         | Open a new channel, and send the first fragment of the
+% OP_STATUS       | Part of a message, but expects an immediate ACK, in case
-%                 | first message in it.
+%                 | the stream goes idle, or for any other
-% OP_END_MESSAGE  | End of a message/stream, expects a response
+%                 | implementation-specific needs.
-% OP_OPEN_END     | Open a new channel, and send an entire message
+% OP_END_MESSAGE  | Last/only fragment of a message/stream. Expects the other
-% OP_CLOSE        | End of a message/stream, do not respond, close the channel
+%                 | side to reply on this channel.
-% OP_OPEN_CLOSE   | Open a channel, send an entire message, and close the
+% OP_CLOSE        | Last/only fragment of a message/stream. Closes the channel.
-%                 | channel, all in one datagram. Sort of like
-%                 | gen_server:cast/2, or if UDP were reliable.
 %
 % Transport Control Stuff
 % -----------------------------------------------------------------------------
 % OP_ACK          | Acknowledge that instructions up to N have been received.
-% OP_STATUS       | Request an ACK for this exact command. Has many uses -
-%                 | diagnostics, benchmarking, keepalive, dropped ACKs, or just
-%                 | to stop the receiver from coalescing ACKs too much.
 % OP_NACK         | Instruction N has not been received.
-% OP_CANCEL       | Sender is hoping that messages M through N weren't
+% OP_CANCEL       | Ignore any fragments that weren't already delivered, and
-%                 | delivered, and can be cancelled.
+%                 | end the stream now. The channel stays open so that the
-% OP_ACK_CANCEL   | Respond to OP_CANCEL.
+%                 | other side can communicate what they did/didn't | receive,
-%
+%                 | and what actions were taken, if the application requires.
-% Stream Negotiation
-% _____________________________________________________________________________
-% OP_REQ_MOVE     | Indicate that a newly opened channel lost the race, and
-%                 | should be moved to a different ID.
 %
 % Lossy
 % _____________________________________________________________________________
@@ -56,20 +53,15 @@
 % OP_LOSSY        | A lossy datagram, for the application to deal with.
 
 % Numbers aren't final.
--define(OP_FRAGMENT,     0).
+-define(OP_FRAGMENT,    0).
--define(OP_OPEN,         1).
+-define(OP_END_MESSAGE, 1).
--define(OP_END_MESSAGE,  2).
+-define(OP_CLOSE,       2).
--define(OP_OPEN_END,     3).
+-define(OP_STATUS,      3).
--define(OP_CLOSE,        4).
+-define(OP_ACK,         4).
--define(OP_OPEN_CLOSE,   5).
+-define(OP_NACK,        5).
--define(OP_ACK,          6).
+-define(OP_CANCEL,      6).
--define(OP_STATUS,       7).
+-define(OP_OPEN_DIRTY,  7).
--define(OP_NACK,         8).
+-define(OP_LOSSY,       8).
--define(OP_CANCEL,       9).
--define(OP_ACK_CANCEL,  10).
--define(OP_REQ_MOVE,    11).
--define(OP_OPEN_DIRTY,  12).
--define(OP_LOSSY,       13).
 
 %%% Type and Record Definitions
 
@@ -80,14 +72,24 @@
          seq :: integer(),
          data :: binary()}).
 
+
+-type request_type() :: fragment | message.
+-type request_recipient() :: {async, pid()} | {sync, gen_server:from()}.
+-record(request,
+        {type :: request_type(),
+         recipient :: request_recipient()}).
+-type request() :: #request{}.
+
 -record(s,
         {chan_id :: integer(),
          socket :: gen_udp:socket(),
          peer :: endpoint(), % TODO configure the socket in advance?
          state = closed :: closed | sending | receiving,
          seq = 0 :: integer(),
+         requests = {[], []} :: {[request()], [request()]},
+         subscriber = none :: none | request(),
          instructions = [] :: [#instruction{}],
-         fragments = [] :: [binary()]}).
+         fragments = {[], []} :: {[binary()], [binary()]}}).
 
 
 -type state() :: none | #s{}.
@@ -102,6 +104,31 @@ configure_channel(Pid, Id, Socket, Peer) ->
 send_and_close(Chan, Message) ->
     gen_server:call(Chan, {send, Message, close}).
 
+send_message(Chan, Message) ->
+    gen_server:call(Chan, {send, Message, end_message}).
+
+receive_fragment(Chan) ->
+    gen_server:call(Chan, {add_sync_request, fragment}).
+
+receive_message(Chan) ->
+    gen_server:call(Chan, {add_sync_request, message}).
+
+subscribe_fragment(Chan) ->
+    Pid = self(),
+    gen_server:call(Chan, {subscribe, fragment, Pid}).
+
+subscribe_message(Chan) ->
+    Pid = self(),
+    gen_server:call(Chan, {subscribe, message, Pid}).
+
+subscribe_fragment_once(Chan) ->
+    Pid = self(),
+    gen_server:call(Chan, {add_async_request, fragment, Pid}).
+
+subscribe_message_once(Chan) ->
+    Pid = self(),
+    gen_server:call(Chan, {add_async_request, message, Pid}).
+
 %%% gen_server
 
 -spec start_link() -> Result
@@ -119,6 +146,15 @@ init(none) ->
 handle_call({send, Message, Mod}, _, State) ->
     {Result, NewState} = do_send(Message, Mod, State),
     {reply, Result, NewState};
+handle_call({add_sync_request, Type}, From, State) ->
+    NewState = do_add_sync_request(Type, From, State),
+    {noreply, NewState};
+handle_call({add_async_request, Type, Pid}, _, State) ->
+    {Result, NewState} = do_add_async_request(Type, Pid, State),
+    {reply, Result, NewState};
+handle_call({subscribe, Type, Pid}, _, State) ->
+    {Result, NewState} = do_subscribe(Type, Pid, State),
+    {reply, Result, NewState};
 handle_call(Unexpected, From, State) ->
     ok = log(warning, "Unexpected call from ~tp: ~tp", [From, Unexpected]),
     {noreply, State}.
@@ -167,25 +203,55 @@ do_send(_, open_dirty, State = #s{state = ChanMode}) when ChanMode /= closed ->
 do_send(_, _, State = #s{state = receiving}) ->
     {{error, not_sending}, State};
 do_send(Message, Mod, State = #s{chan_id = Id,
-                                 state = ChanMode,
                                  peer = Peer,
                                  socket = Sock,
                                  seq = Seq}) ->
     log(debug, "~p is sending a message to ~p, seq ~p~n", [self(), Peer, Id]),
-    IsNewChannel = ChanMode == closed,
+    {Op, NewChanMode} = choose_opcode(Mod),
-    {Op, NewChanMode} = choose_opcode(IsNewChannel, Mod),
     Datagram = <<Id:8, Op:8, Seq:16, Message/bytes>>,
     gen_udp:send(Sock, Peer, Datagram),
     NewState = State#s{state = NewChanMode, seq = Seq + 1},
     {ok, NewState}.
 
-choose_opcode(false, none)        -> {?OP_FRAGMENT,    sending};
+choose_opcode(none)        -> {?OP_FRAGMENT,    sending};
-choose_opcode(true,  none)        -> {?OP_OPEN,        sending};
+choose_opcode(end_message) -> {?OP_END_MESSAGE, receiving};
-choose_opcode(false, end_message) -> {?OP_END_MESSAGE, receiving};
+choose_opcode(close)       -> {?OP_CLOSE,       closed};
-choose_opcode(true,  end_message) -> {?OP_OPEN_END,    receiving};
+choose_opcode(open_dirty)  -> {?OP_OPEN_DIRTY,  sending}.
-choose_opcode(false, close)       -> {?OP_OPEN_END,    closed};
+
-choose_opcode(true,  close)       -> {?OP_OPEN_CLOSE,  closed};
+%%% Subscription Doer Functions
-choose_opcode(true, open_dirty)   -> {?OP_OPEN_DIRTY,  sending}.
+
+% Adds a request to the queue, or responds to that request directly, if there
+% is a subscriber already.
+do_add_sync_request(Type, From, State = #s{subscriber = none}) ->
+    do_add_request(Type, {sync, From}, State);
+do_add_sync_request(_, From, State) ->
+    Result = {error, already_subscribed},
+    gen_server:reply(From, Result),
+    State.
+
+% Adds a request to the queue and returns ok, or returns an error if there is a
+% subscriber already.
+do_add_async_request(Type, Pid, State = #s{subscriber = none}) ->
+    NewState = do_add_request(Type, {async, Pid}, State),
+    {ok, NewState};
+do_add_async_request(_, _, State) ->
+    Result = {error, already_subscribed},
+    {Result, State}.
+
+do_add_request(Type, Recipient, State = #s{requests = {In, Out}}) ->
+    Request = #request{type = Type, recipient = Recipient},
+    NewRequests = {[Request | In], Out},
+    StateWithRequest = State#s{requests = NewRequests},
+    try_fill_requests(StateWithRequest).
+
+do_subscribe(Type, Pid, State = #s{subscriber = none}) ->
+    Request = #request{type = Type, recipient = {async, Pid}},
+    StateWithSub = State#s{subscriber = Request},
+    NewState = try_fill_requests(StateWithSub),
+    {ok, NewState};
+do_subscribe(_, _, State) ->
+    Result = {error, already_subscribed},
+    {Result, State}.
 
 %%% Receive Doer Functions
 
@@ -198,11 +264,6 @@ do_handle_datagram(State, <<?OP_NACK:8, Data/binary>>) ->
     do_handle_nack(State, Data);
 do_handle_datagram(State, <<?OP_CANCEL:8, Data/binary>>) ->
     do_handle_cancel(State, Data);
-do_handle_datagram(State, <<?OP_ACK_CANCEL:8, Data/binary>>) ->
-    % TODO: do we need ack cancel? There isn't much you can do with the
-    % sequence information, you really just need the server to tell you what
-    % did get through and how it was interpreted.
-    do_handle_ack_cancel(State, Data);
 do_handle_datagram(State, <<Op:8, Seq:16, Rest/binary>>) ->
     log(debug, "Got opcode ~p, seq ~p. Adding to buffer.~n", [Op, Seq]),
     % Reliable stream operations need to be ordered first.
@@ -228,10 +289,6 @@ do_handle_cancel(State, Payload) ->
     io:format("Unimplemented command. Data ~p~n", [Payload]),
     State.
 
-do_handle_ack_cancel(State, Payload) ->
-    io:format("Unimplemented command. Data ~p~n", [Payload]),
-    State.
-
 %%% Reliable message reordering
 
 do_buffer_reliable(State = #s{instructions = Is}, Op, Seq, Rest) ->
@@ -251,45 +308,132 @@ insert_instruction(Op, Seq, Data, Is, Earlier) ->
 
 %%% Reliable message execution
 
-do_execute_buffer(State = #s{seq = Seq, instructions = [#instruction{op = Op, seq = Seq, data = Data} | Rest]}) ->
+do_execute_buffer(State = #s{state = closed, seq = Seq, instructions = [#instruction{seq = Seq} | _]}) ->
+    % If we are closed, then anything we receive opens the channel.
+    StateOpened = State#s{state = receiving},
+    do_execute_buffer(StateOpened);
+do_execute_buffer(State = #s{state = receiving, seq = Seq, instructions = [#instruction{op = Op, seq = Seq, data = Data} | Rest]}) ->
     PoppedState = State#s{instructions = Rest, seq = Seq + 1},
+    log(debug, "Executing instruction. Op: ~p, Seq: ~p.~n", [Op, Seq]),
     NewState = do_handle_reliable(PoppedState, Op, Seq, Data),
     do_execute_buffer(NewState);
 do_execute_buffer(State) ->
-    % Empty instruction list, or the next instruction hasn't arrived yet. Done.
+    % We've finished consuming instructions; now see if we have any requests we
-    State.
+    % can fill.
+    try_fill_requests(State).
 
 do_handle_reliable(State, ?OP_FRAGMENT, Seq, Payload) ->
-    do_handle_fragment(State, false, continue, Seq, Payload);
+    do_handle_fragment(State, continue, Seq, Payload);
-do_handle_reliable(State, ?OP_OPEN, Seq, Payload) ->
-    do_handle_fragment(State, true, continue, Seq, Payload);
 do_handle_reliable(State, ?OP_END_MESSAGE, Seq, Payload) ->
-    do_handle_fragment(State, false, end_message, Seq, Payload);
+    do_handle_fragment(State, end_message, Seq, Payload);
-do_handle_reliable(State, ?OP_OPEN_END, Seq, Payload) ->
-    do_handle_fragment(State, true, end_message, Seq, Payload);
 do_handle_reliable(State, ?OP_CLOSE, Seq, Payload) ->
-    do_handle_fragment(State, false, close_channel, Seq, Payload);
+    do_handle_fragment(State, close_channel, Seq, Payload);
-do_handle_reliable(State, ?OP_OPEN_CLOSE, Seq, Payload) ->
-    do_handle_fragment(State, true, close_channel, Seq, Payload);
 do_handle_reliable(State, ?OP_STATUS, Seq, Payload) ->
     do_handle_status(State, Seq, Payload);
-do_handle_reliable(State, ?OP_REQ_MOVE, Seq, Payload) ->
-    do_handle_req_move(State, Seq, Payload);
 do_handle_reliable(State, ?OP_OPEN_DIRTY, Seq, Payload) ->
-    do_handle_fragment(State, true, dirty, Seq, Payload);
+    do_handle_fragment(State, dirty, Seq, Payload);
 do_handle_reliable(State, Unknown, _, _) ->
     io:format("Got unexpected opcode ~p~n", [Unknown]),
     State.
 
-do_handle_fragment(State, NewChannel, Mod, Seq, Payload) ->
-    io:format("Got fragment ~p with index ~p, and flags ~p and ~p~n", [Payload, Seq, NewChannel, Mod]),
-    State.
-
 do_handle_status(State, Seq, Payload) ->
-    io:format("Unimplemented command. Index ~p, payload ~p~n", [Seq, Payload]),
+    send_ack(State, Seq),
-    State.
+    do_handle_fragment(State, continue, Seq, Payload).
 
-do_handle_req_move(State, Seq, Payload) ->
+send_ack(#s{chan_id = ID, socket = Sock, peer = Peer}, Seq) ->
-    io:format("Unimplemented command. Index ~p, payload ~p~n", [Seq, Payload]),
+    % TODO: backpressure
-    State.
+    gen_udp:send(Sock, Peer, <<ID:8, ?OP_ACK:8, Seq:16>>).
+
+do_handle_fragment(State, Mod, _Seq, Payload) ->
+    WithFragment = push_fragment(State, Payload),
+    update_chan_mode(WithFragment, Mod).
+
+push_fragment(State = #s{fragments = {In, Out}}, Payload) ->
+    State#s{fragments = {[Payload | In], Out}}.
+
+update_chan_mode(State, continue) ->
+    State#s{state = receiving};
+update_chan_mode(State, end_message) ->
+    State#s{state = sending};
+update_chan_mode(State, close_channel) ->
+    % TODO: Properly clean up subscriptions and requests and things, if the
+    % channel closes... Also if the channel switches to sending, I guess a
+    % fragment subscriber should be notified?
+    State#s{state = closed};
+update_chan_mode(State, dirty) ->
+    % TODO: create and then quarantine dirty channels
+    State#s{state = receiving}.
+
+try_fill_requests(State = #s{requests = Requests}) ->
+    case pop_queue(Requests) of
+        {ok, {Remaining, Request}} ->
+            try_fill_requests2(State, Remaining, Request);
+        error ->
+            % No requests, try subscriptions instead.
+            try_fill_subscription(State)
+    end.
+
+try_fill_requests2(State, RequestsRemaining, Request) ->
+    Without = State#s{requests = RequestsRemaining},
+    case try_fill_request(Without, Request) of
+        {ok, NewState} ->
+            % Done successfully! Start the loop again with the new state.
+            try_fill_requests(NewState);
+        error ->
+            % The request didn't get filled... Just revert.
+            State
+    end.
+
+try_fill_subscription(State = #s{subscriber = none}) ->
+    % No subscription either! Do nothing.
+    State;
+try_fill_subscription(State = #s{subscriber = Sub}) ->
+    % A subscription! Try to fill it as many times as possible.
+    try_fill_subscription_loop(State, Sub).
+
+try_fill_subscription_loop(State, Sub) ->
+    case try_fill_request(State, Sub) of
+        {ok, NewState} ->
+            try_fill_subscription_loop(NewState, Sub);
+        error ->
+            State
+    end.
+
+try_fill_request(#s{state = receiving}, #request{type = message}) ->
+    % Message not finished yet.
+    error;
+try_fill_request(#s{fragments = {[], []}}, #request{type = message}) ->
+    % No fragments have been received, not even empty fragments. This
+    % channel/message hasn't even been opened yet.
+    error;
+try_fill_request(State = #s{fragments = {In, Out}}, #request{type = message, recipient = Recip}) ->
+    Fragments = Out ++ lists:reverse(In),
+    Message = list_to_binary(Fragments),
+    send_result(Recip, Message),
+    NewState = State#s{fragments = {[], []}},
+    {ok, NewState};
+try_fill_request(State = #s{fragments = Fragments}, #request{type = fragment, recipient = Recip}) ->
+    case pop_queue(Fragments) of
+        {ok, {NewFragments, Fragment}} ->
+            log(debug, "Replying to fragment request. Fragment: ~p~n", [Fragment]),
+            send_result(Recip, Fragment),
+            NewState = State#s{fragments = NewFragments},
+            {ok, NewState};
+        error ->
+            State
+    end.
+
+send_result({async, Pid}, Result) ->
+    erlang:send(Pid, {msp_fragment, self(), Result});
+send_result({sync, From}, Result) ->
+    gen_server:reply(From, {ok, Result}).
+
+pop_queue({[], []}) ->
+    error;
+pop_queue({In, [Next | Out]}) ->
+    NewFragments = {In, Out},
+    {ok, {NewFragments, Next}};
+pop_queue({In, []}) ->
+    Out = lists:reverse(In),
+    pop_queue({[], Out}).
 

src/msp_tests.erl

@@ -21,8 +21,8 @@ run_tests_protected() ->
     end.
 
 run_tests() ->
-    %ok = send_test(),
+    ok = send_test(),
-    %ok = out_of_order_test(),
+    ok = out_of_order_test(),
     ok = race_test(),
     ok.
 
@@ -37,15 +37,21 @@ send_test() ->
     ok = make_connection(PortA, IP, PortB, 0),
     ok = make_connection(PortB, IP, PortA, 1),
 
-    {ok, {ChanA, IndexA}} = msp_channel_man:create_channel(PortA, IP, PortB),
+    {ok, {ChanA, 0}} = msp_channel_man:create_channel(PortA, IP, PortB),
-    msp_channel:send_and_close(ChanA, <<"message sent from A to B">>),
+    {ok, {ChanB, 0}} = msp_channel_man:create_channel(PortB, IP, PortA),
-    io:format("A has tried to send a message on channel ~p~n", [IndexA]),
+
-    timer:sleep(10),
+    MessageA = <<"message sent from A to B">>,
+    msp_channel:send_and_close(ChanA, MessageA),
+    io:format("A has tried to send a message to B~n"),
+    {ok, MessageA} = msp_channel:receive_message(ChanB),
+    io:format("received successfully~n"),
+
+    MessageB = <<"message sent from B to A">>,
+    msp_channel:send_and_close(ChanB, MessageB),
+    io:format("B has tried to send a message to A~n"),
+    {ok, MessageB} = msp_channel:receive_message(ChanA),
+    io:format("received successfully~n"),
 
-    {ok, {ChanB, IndexB}} = msp_channel_man:create_channel(PortB, IP, PortA),
-    msp_channel:send_and_close(ChanB, <<"message sent from B to A">>),
-    io:format("B has tried to send a message on channel ~p~n", [IndexB]),
-    timer:sleep(10),
     ok.
 
 out_of_order_test() ->
@@ -54,14 +60,13 @@ out_of_order_test() ->
     PortB = 5522,
     {ok, SockA} = gen_udp:open(PortA),
     ok = make_connection(PortB, IP, PortA, 0),
+    {ok, {ChanB, 0}} = msp_channel_man:create_channel(PortB, IP, PortA),
 
-    % TODO: fix race_test and remove this sleep
+    ok = gen_udp:send(SockA, {IP, PortB}, <<0:8, 2:8, 1:16, "second fragment;">>),
-    timer:sleep(10),
+    ok = gen_udp:send(SockA, {IP, PortB}, <<0:8, 0:8, 0:16, "first fragment;">>),
 
-    ok = gen_udp:send(SockA, {IP, PortB}, <<0:8, 4:8, 1:16, "second message">>),
+    {ok, <<"first fragment;second fragment;">>} = msp_channel:receive_message(ChanB),
-    ok = gen_udp:send(SockA, {IP, PortB}, <<0:8, 1:8, 0:16, "first message">>),
+    io:format("Received out of order fragments successfully.~n"),
-
-    timer:sleep(10),
 
     ok.
 
@@ -71,12 +76,18 @@ race_test() ->
     PortB = 5532,
     {ok, SockA} = gen_udp:open(PortA),
     {ok, SockB} = gen_udp:open(PortB, [{active, true}]),
-    ok = gen_udp:send(SockA, {IP, PortB}, <<0:8, 5:8, 0:16, "a message">>),
+    ok = gen_udp:send(SockA, {IP, PortB}, <<0:8, 2:8, 0:16, "a message">>),
 
     timer:sleep(10),
 
+    % We should already have a {udp, SockB, IP, PortA, _} in our message queue,
+    % which needs to be properly detected and handled by the socket transfer
+    % functions.
     ok = msp_channel_man:add_route(SockB, IP, PortA, 0),
 
+    % TODO We could test that the datagrams were dispatched properly by
+    % receiving on the channel, but for now we just manually check the
+    % logs/console output for msp_channel_man errors.
     timer:sleep(10),
 
     ok.